The present invention relates generally to communication networks, and more specifically, to a dense wavelength division multiplexing (DWDM) system configured to support IP telephony at remote equipment site locations.
Historically service providers have used several layers of equipment to construct high-speed data networks (e.g., routers over ATM switches over Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) network elements). Each piece of equipment performs a unique function. For example, ATM switches enable traffic engineering and SONET/SDH network elements provide performance monitoring and ring-based protection. A large amount of equipment is needed under this model, and the cost of delivering data services in this manner is very high. Constant upgrades are required for all of these network elements as the network grows, thus, the model does not scale well.
Furthermore, since optical signals become attenuated as they travel through fiber they must be periodically regenerated in core networks. In SONET/SDH optical networks each separate fiber carrying a single optical signal requires a separate electrical regenerator every 60 to 100 km. As additional fibers are added in a core network, the total cost of regenerators becomes very large. The regenerator receives a modulated optical signal, transforms it to an electronic signal, amplifies it, and then converts the electronic signal back to an optical signal of the same modulation and bit rate. Regenerators only amplify a single wavelength. Therefore, considering that in an optical link there are several regenerators, in a multiwavelength fiber system the maintenance cost is significant.
DWDM technologies allow IP service providers to achieve functionality without the expense of deploying SONET/SDH and ATM equipment or protocols. Wavelength Division Multiplexing (WDM) is an optical technology that couples many wavelengths in the same fiber, thus effectively increasing the aggregate bandwidth per fiber to the sum of the bit rates of each wavelength. Dense WDM (DWDM) is a technology with a larger (denser) number of wavelengths (e.g., >40) coupled into a fiber than WDM. Systems may support, for example, 100 wavelengths per fiber, enabling a single fiber to carry several hundred gigabits of information. DWDM increases the capacity of embedded fiber by first assigning incoming optical signals to specific frequencies within a designated frequency band and then multiplexing the resulting signals out onto one fiber. DWDM combines multiple optical signals so that they can be amplified as a group and transported over a single fiber to increase capacity. Each signal can be at a different rate and in a different format. DWDM applications include ultra-high bandwidth long haul as well as ultra-high-speed metropolitan or inner city-networks, and at the edge of other networks such as SONET, Internet protocol (IP) and asynchronous transfer mode (ATM).
Long-haul DWDM systems take standard optical signals from elements such as SONET/SDH network elements, IP routers, or ATM switches and convert each signal to a distinct, precise wavelength (e.g., in the 1530 to 1610 nm range). These individual wavelengths are then combined (optically multiplexed) onto a single fiber. In the receive direction of the system, the reverse process takes place. Individual wavelengths are filtered from the multiplexed fiber and converted back to a standard signal to the client. The complete DWDM system typically includes modules for each client interface in addition to equipment for multistage optical combining or splitting of wavelengths, amplification, and management/control.
DWDM systems reduce the need for and cost of electrical regeneration over long distances. As a result, virtually all operators of long distance fiber optic networks have implemented or expect to implement DWDM. The introduction of optical amplifiers in conjunction with DWDM systems has significantly reduced the cost of long-haul transmission. A single optical amplifier is able to reamplify all of the channels on a DWDM fiber without demultiplexing and processing them individually. The optical amplifier merely amplifies the signals, and does not reshape, retime, or retransmit them as a regenerator does. The signals may still need to be regenerated periodically, however, this can now be done approximately every 1000 kilometers. One optical amplifier can thus replace about 40 separate regenerators.
Since the channels are not demultiplexed at locations of optical amplifiers, a data channel is not typically available at remote geographic locations where the optical amplifier is located. If data access is required at these remote locations additional equipment is required to separate and pull off one or more channels. Furthermore, if voice communication is required, a public telephone line must be installed at each remote line site.
There is, therefore, a need for a system and method for providing data and voice access at optical amplifier location sites without the need for additional demultiplexing equipment or telephone lines.